The Army veteran who drove a truck into a crowd of New Year’s revellers in New Orleans acted alone, the FBI said on Thursday, reversing its position from a day earlier that he likely worked with others in the deadly attack that officials said was inspired by the Islamic State group.

The FBI also revealed that the driver, Shamsud-Din Jabbar, an American citizen from Texas, posted five videos on his Facebook account in the hours before the attack in which he proclaimed his support for the militant group and previewed the violence that he would soon unleash in the famed French Quarter district.

“This was an act of terrorism. It was premeditated and an evil act,” said Christopher Raia, the deputy assistant director of the FBI's counterterrorism division, calling Jabbar “100 per cent inspired” by the Islamic State.

The attack along Bourbon Street killed 14 revellers, along with Jabbar, 42, who was fatally shot in a firefight with police after steering his speeding truck around a barricade and ploughing into the crowd. About 30 people were injured.

Raia stressed there was no indication of a connection between the New Orleans attack and the explosion on Wednesday of a Tesla Cybertruck filled with explosives outside Trump’s Las Vegas hotel.

The person inside that truck, a decorated US Army Green Beret, shot himself in the head just before detonation, authorities said. (AP)